Page:Philosophical Transactions - Volume 001.djvu/229

 Variation of the Altitude of the Mercurial Cylinder, which at most is hardly three Inches, may be made as distinguishable, as if it were three Foot, or three Yards, or as much more, as is desired. The manner hereof is visible enough by Figure I: where A B C represents the Tube, which may be either Blunt, or with a Head, as A B C (by which latter shape, more room is allow'd for any remainder of Air, to expand the better.) This is to be filled with Quick-silver, and inverted as commonly; but into a Vessel of Stagnant Mercury, made after the fashion of I K, that is, having its sides about 3 or 4 inches high, and the Cavity of it equally big both above and below; and if it can be (besides that part, which is fill'd by the end of the Mercurial Tube, that stands in it) of equal capacity with the hollow of the Cane about B: For then the Quicksilver rising as much in the hollow of I, as it descends at B, the difference of the height in the Receiver I, will be just half the usual difference. And if the receiving Vessel I K have a bigger Cavity, the difference will be less, but if less, the difference will be greater: But, whether the difference be hereby made bigger or less, 'tis no great matter, since by the contrivance of the Wheel and Index which is more fully described in the Preface to the Micrography the least variation may be made as sensible as is desired, by diminishing the bigness of the Cylinder E, and lengthening the Index F G, according to the Proportion requisite.

These Phænomena are thought worthy to be inserted here, for the Speculation of the Curious in those Kingdoms; as they were publisht in the French Journal des Scavans, of May 10. 1666. viz.

The 9th of April of this present year, about half an hour past nine, there appear'd three Circles in the Sky. One of them was very great, a little interrupted, and white every where, without Rh